Mechanical type thermometer



1954 J. w. DICKEY ETAL 2,691,891

MECHANICAL TYPE THERMOMETER Filed Dec. 11, 1951 2 Sheets-Sheet l I I Ill] I? INVENTORS WITNESS: BY '6: Wood 2 Sheets-Sheet 2 AOHNEY 1954 J. w. DlCKEY ETAL MECHANICAL TYPE THERMOMETER I} KNEW WEEK WTNESS.

Patented Oct. 19, 1954 EIECHANICAL TYPE THERMOMETER John W. Dickey, Newfield, and E. Elliott Hood, Elmira, N. Y., assignors to Bendix Aviation Corporation, a corporation of Delaware Application December 11, 1951, Serial No. 261,092

The present invention relates to a mechanical typ thermometer, and more particularly to a thermometer in which the heat-responsive element is in the form of a tubular spiral of bimetallic material.

The thermometer here disclosed is intended primarily for use in situations where it is subject to rapid fluctuations of temperature over a very wide range, as encountered in apparatus for determining the freezing point of liquids, such as disclosed in the co-pending application of Dickey, Serial No. 83,986, filed March 28, 1949, now U. S. Patent No. 2,633,736, and assigned to the assignee of the present application.

It is an object of the present invention to provide a thermometer of the above type in which the heat-sensitive element is located in a stem remote from the registering part of the thermometer, and incorporating novel means for reducing the transmission of heat from the body of the thermometer to the heat-sensitive element.

It is another object to provide such a device having novel means for anchorage of the heatsensitive element in the thermometer stem, and for calibrating and adjusting the thermometer.

Further objects and advantages will be apparent from the following description taken in connection with the accompanying drawing in which:

4 Claims. (Cl. 73--367) Fig. l is a vertical substantially mid-sectional view of a preferred embodiment of the invention;

dial 2 is fixedly mounted in any suitable manner as indicated at 3. A hollow stem 6 is rigidly mounted on the casing l substantially normal thereto and co-axial therewith as indicated at 5, and a needle staif 6 is freely journalled in the stem b means of bearings '21 and 8, and has an indicating needle 9 fixedly mounted on one end thereof within the casing l in operative relation with the dial 2. The thermometer stem is enclosed in a flanged heat-exchange tube In which provides an annular space around the stem for receiving the liquid whose freezing point is to be determined as set forth in the Dickey application above cited.

A heat-sensitive element H in the form of a tubular spiral of bi-metallic ribbon having spaced convolutions is located in the thermometer stem 5, rigidly connected at one end to the free end of the stem, and coupled at its other end to the needle staff 6.

The connection between the heat-sensitive element H and the stem 4 is effected as shown in Fig. 2 by means of a metallic cup member l2, soldered in the end of the stem, snugly receiving the end of the spiral H and rigidly connected therewith by means of a slug it of comparatively soft material such as copper which is expanded laterally by end-wise pressure so as to force the spiral outward into a firm anchored relation with the cup.

The connection between the bi-metallic spiral H and the needle staff 6 is so constructed as to provide for convenient and accurate calibration of the heat-sensitive element, and for permanent retention of the calibration. For this purpose, the end of the needle staff 5 has a screw memher [4 rigidly mounted thereon in any suitable manner as by soldering, which screw member has a thread [5 having the same pitch as the spiral l I and slideably engaging between the spaced convolutions of the spiral. Rotation of the needle stem and screw member with respect to the heatsensitive element therefore moves the screw member longitudinally so as to vary the eilective length of the heat-sensitiv element, and consequently vary the ratio between change of temperature and the angular movement of the needle caused thereby. In order to immobilize this connection after adjustment has been secured, a cup member to is mounted on the end of the needle staff 6 so as to overlap the screw member I4 and the end of the bi-metallic spiral, and relative rotation of the parts is prevented by staking the parts together by displacing one or more portions of the cup l6 inwardly. The thread I5 of screw member It is preferably formed with a sharp edge or crown as illustrated so that when the cup I6 is pressed inward, the thread cuts into the interior ofthe cup so as to form a permanent rigid connection.

In the assembly of the instrument, one end of the heat sensitive element H is first introduced into the cup I2, the slug i3 is dropped in place and then expanded by a blow or pressure exerted through a suitable mandrel inserted in the bimetallic element, so as to form a rigid swaged connection. The needle staff 6, with the screw the dial 2. The cup I2 is then permanently'con nected to the free end of the stem 4 as by'soldermg.

Itwillbe particularly noted that since,.when the thermometer is in use, the stem 4 is incontact withthe fluid whose temperature is to be measured, and since the heat-sensitive element I is. only connecteditdthe stem at itsouter end, there will be no transmission of heat betweenthe body. of the casing I of thethermometer and the heat sensitive element through the stem.4-, as. Wouldbe the case if theheat-sensitive element were. connected to the stem at. its other end.

Transmissionof heat to or. from the.heat-sensi--- tive element through the needle sta-fi 6. is minimizedby making thebearingsl and 8 of insulating. material, and the stall. itself is preferably. made of .a material such as a stainless steelhaving a. comparativelyhighresistance to.-the con.- duction of heat. By this arrangement, the heat.- sensitive element faithfully follows the changes in. temperature of. the adjacent. portion. of the thermometer stem 4 without the introduction of errors due to heat conduction. from the body of the thermometer.

InEigs. 3 and 4 of the drawing there is illustrated a second embodiment of the invention incorporating modifications in the meansfor. an--- choring the. temperature-sensitive element. and.

for coupling it to the needle staff of the thermometer.

In this. embodiment, the parts of the indicating. portion of the thermometer including the.

casing, dial, needle, stem and needle stafi are the sameas in the first embodiment and are similar-- 1y. numbered.

In; thiscase, however, the heatesensitive. element 2| is spot-welded to the needle staff .6. asindicatedat 22 at the end adjacent to thebody. of the thermometer, this end being maintainedin.

coaxial relation with the stem.4 of. the thermom:

When this adjustment has been see.

The assembly is thenslid into'rthe ther-- mometer stem 4, the needle 9fis mounted .on-the stem 8 and the assembly is rotatedcint'o. position; to properly indicate the existingtemperatureon.

eter by meansof a cup-shaped bearing Z3 having a slightly elastic rim, which is pressed into the stem dwhen the device is. assembled.

The opposite end of the heat sensitive element 21 is mounted on a plug member 24 having areduced extension 25 provided with a thread 26 slidably engaging between the convolutions of the heat-sensitive element.

Means are provided for anchoring the heat sensitive element in adjusted position on the plug. 24, such means being here illustrated in the form of a sleeve 2] of somewhat smaller diameter thanv the main portion of the plug 24 and having a sliding fit over the end of the heat-sensitive element. The anchorage of these members is secured by pressing the sleeve 2'! inwardly atone or more 10- cations as indicatedat 28..so as toform a rigid connection between the heat-sensitive element and the plug. Alternatively, the heat-sensitive element 2| may be anchored in the plug 24 by spot-welding in its adjusted position.

In the assembly of this embodiment of the invention, the needle staff 6 is welded to the free end of the heat sensitive element 2|; the sleeve 21-?! iswslid on the other end ofi'the' bi-metallic spiral and the latter iso-threa-dedon the plug. The subassembly is then mounted in a calibrating fixture and the spiral is adjusted on the plug until its efiectivelength is such as to secure the desired relationship between the angular rotation of the needle-stafiiand'theohange of temperature correspondingthereto; When this adjustment is secured; th'e=sleeve Z-Fis staked to the spiral 2| and the plugas indicatedlat 28, or the bimetal is spotwelded to the plug,and the assembly is inserted in-thestem 4 of the thermometer. The plug 24 is then permanently connected to the end of the stem -in.'any suitable manner-as by-soldering. The needle; 9, which .is preferably frictionally mounted onthe freeend ofthestafffi similarlyto-the conventionalmanner of mounting the hands of .a clock, is then adjusted on its staffsoas to indi-- cate 'theprevailing. temperature on the -scale- 2. Although pertain-embodiments of the inventionhave been-shown. and described in detail, it willbe understood that other embodiments are; possible and changes. mayrbe made .in the precise formand arrangement/ofthe parts without-de par-ting from the spirit of Y the invention.

Weclaim: 1. In a mechanical typethermometer acasing, an: arcuate dial-fixedly mounted inthe casing,- a tubular-stem;- mounted. on the. casing normal. to and coaxial with the. diaLa-stafirotatably mount? edin the stem. projecting into, the. casing and. havinga needle fixedthereon in..cooperative=re:-.- lation-to the dial, aspiral-of bimetallicribbon-inthe stem, and means. for: anchoring one :end .of the.- spiral to theouter end-of said-stem, and-theother end\ of the-spiralto: the outer, end.- of the needle: staff; the spiral. of bimetallic ribbon being, formed with uniformly spaced: convolutions, and:- means. for adjusting the free length-of thespiral between. said. anchorages: toxvary the ratio be. tween temperature changeof. therspiraliandconasequent angular movement of the needle comprise ing-an. anchoring;- plug. in one. end. of the spiral having; a: thread nof-the. same pitcn flSxSklldtspiTfiil: and: slidable: in the: spacesrbetween-the; convolutions; and; means" including: a: sleeve surrounding". and compressing the;bim'etallicispira1 for: immo:-.- bilizing the threadedconne'ction between the plug and bimetallic spiral-in adjusted position."

2C In a mechanical type thermometer; a casing; a hollow cylindrical stem fixed at one endto'the casing and extending substantially normal there'- to, a tubular'spiral of bi metallic ribbon'in said stem'having spaced convolutions, a cup member fixedly. mounted on one end offthe biI-metallic spiral; means anchoring said cup in the other. end of. said' stem, a needle .stafi'rotatably mounted in the stem and extendingintothe casing, a threadedconnection between thestafiand'tl'ie otherendl of the. bi-metallic spiral; and.means.for immobi lizing the threaded connection; in which the threaded'connection between the needle staff and the bi-metallic spiral comprises. an adjusting. screw member fixedly mounted.on..saidlstafil'having a thread slidably engaging the spaced'.convolutions of .tlie spiral'andla cup fittingover-the.

end ofthe spiral, overlapping the screw member" and having a portion displaced inwardly to hold the connection in adjusted position.

3. A thermometer as set forth in claim 2 in which the thread of the adjusting nut has a sharp crown which cuts into the interior of the cup where the cup is displaced inwardly.

4. A mechanical type thermometer including a rotatable needle stafi, means including a spiral of bi-metallic ribbon for rotating the staff in response to changes of temperature, and means for adjusting the effective length of the spiral including a mounting and connecting element threaded into one end of the spiral and a deformable sleeve surrounding and compressing the threaded connection for immobilizing it in adjusted position.

References Cited in the file of this patent UNITED STATES PATENTS Number Number Name Date St. John Oct. 27, 1885 Haight May 17, 1887 Haight Dec. 16, 1890 Ewing Feb. 24, 1920 Ford May 27, 1941 FOREIGN PATENTS Country Date Great Britain June 30, 1939 Great Britain Mar. 31, 1944 

